"No!" Sander became frightened and hastily reacted. Then he was worried that if he denied her entirely, she would be angered or irritated, so he added
"How do I know it's not a poison or even you've been sent by the king of Everlight?"
Sander wasn't going to drink an unknown liquid just because she said so. Occasionally Sander would gamble if the odds are pretty good but in this scenario it's not as there were many variables like the obvious what if the liquid is a poison? and even if he drank the liquid what's the outcome would be?
"It won't kill you immediately after you swear your allegiance before my lord, he will give you the antidote as simple as that"
despite Sander's disapproval the woman before him didn't get angry, rather she still continued to talk with him in a calm tone.